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Full text of "Experiments in preventing the build-up of insects in newly harvested wheat"

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November 1952 E-850 

United States Department of Agriculture 

Agricultural Research Administration 

Bureau of Entomology and Plant Quarantine 


By Gailen D. White 
Division of Stored Product Insect Investigations 

An effective method of preventing the build-up of insects in newly 
harvested wheat has long been needed. Normally wheat is not infested 
in the field, but after it is harvested insects may begin an infestation 
by moving into the wheat from hiding places in the storage bin such as 
cracks or tunnels, or from waste grain, feed rooms, and other nearby 
sources. It has been observed that stored-grain insects can multiply 
themselves more than 40 times in farm -stored wheat during the first 
4 months of storage in wooden farm granaries. 

After the wheat is harvested, the insects have from 3 to 6 months 
in which they can multiply rapidly before winter temperatures cool the 
wheat. A means to prevent the increase of insects in the grain during 
the post-harvest period is therefore highly desirable. 

Dusts have been employed for the protection of seed for many years, 
but the materials used are not suitable for grain intended for feed or 
food, because of their toxic nature. Recently dusts containing pyrethrum 
and similar materials have been considered, since they would not be 
harmful to animals or humans in the amounts used. It is not feasible to 
add inorganic diluents to commercial stocks of grain, since they tend to 
lower the grade, being indistinguishable from lime or other foreign 
matter causing down-grading. It has also been found that insecticidal 
sprays applied to the walls and floors of wooden storage bins before 
being filled are very helpful in reducing initial infestation from these 

Therefore, in the summer of 1951 tests were made in farm bins in 
Reno County, Kans., to determine the effectiveness of (1) insecticidal 
sprays applied to interior walls of wooden farm granaries, (2) fumigants 
applied late in August, and (3) synergized-pyrethrum dusts in preventing 
population build-up in newly harvested wheat. Where bins were sprayed, 
a water emulsion containing 0.2 percent of pyrethrins and 2 percent of 
piperonyl butoxide was applied at the rate of 1 gallon per 1, 000 square 
feet of wall area, or a 2.5-percent water suspension of DDT applied at 
the rate of 2 gallons per 1,000 square feet. The bins in the fumigation 

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series were fumigated with a 3:1 mixture of ethylene dichloride and 
carbon tetrachloride, applied at the rate of 6 gallons per 1,000 bushels 
of wheat. The protectant dust contained 0.08 percent of pyrethrins and 
1.1 percent of piperonyl butoxide— 'in a wheat-dust diluent. It was applied 
at the rate of 75 pounds per 1,000 bushels. 

The tests were grouped into six series as follows: 

1. Control, no treatment (19 bins). 

2. Fumigation late in August (12 bins). 

3. DDT spray on walls (9 bins) 

4. Pyrethrum -piperonyl butoxide spray on walls (8 bins). 

5. Pyrethrum -piperonyl butoxide dust in wheat (9 bins). 

6. Pyrethrum-piperonyl butoxide spray on walls, pyrethrum - 

piperonyl butoxide dust in wheat (7 bins). 

In series 5 the wheat was treated with a special applicator attached 
to a portable auger-type elevator, by which the rate of dust flow was 

In series 6 the dust was applied to the wheat by the individual farmers 
as the bins were filled with whatever equipment they had at hand. Some 
of these bins were filled by auger-type grain elevators, and the dust was 
introduced as the grain was dumped from the truck to the auger so that 
the mixing of dust with grain was done by the auger. In other bins the 
dust was added to the grain stream as it was dumped from the truck into 
the pit of a stationary bucket-type farm grain elevator. After the bins 
were filled with the treated grain, the grain surfaces were "capped" to 
a depth of 3 inches with the dust applied at twice the experimental rate, 
or 150 pounds per 1,000 bushels. 

The original moisture content was determined for each bin. Once a 
month each bin was sampled at three locations with a 5 -foot grain trier, 
or probe. The total number of insects present regardless of species 
was recorded for each sample. For series 1 to 5 observations were 
terminated in September, since the grain was either sold or used for 
seeding purposes. It was possible to take October records for series 6. 
Control bins were sampled to indicate the normal increase in insect 
population over this period. The September population levels were used 
as the measure of effectiveness of the various treatments, since insect 
populations in farm- stored grain in Kansas have usually reached their 
peak by that time. 

1/ This material was furnished by U. S. Industrial Chemicals Co. 
Baltimore, Md. 

- 3 - 

The average original moisture content and the average number of 
insects per 1,000 grams of wheat for each series of bins are given in 
table 1. The bins in the control series developed the greatest population, 
i.e., 41.4 insects per 1,000 grams. The populations in all the treated 
bins were significantly lower than in the control series at the 1 percent 
level of significance. 

The bins fumigated late in August had the lowest population in 
September. Those treated with dust gave the next best results. Insect 
populations were not significantly lower in dusted wheat in sprayed bins 
than in those receiving dust only. The October sampling in series 6 
showed an increase in population, but this increase was entirely in one 
bin in the series. The bin receiving DDT wall spray averaged consider- 
ably lower in insect population than the one sprayed with the pyrethrum- 
piperonyl butoxide mixture. 

Samples of dust-treated wheat from bins in series 5 and 6 were 
submitted to the Kansas State Grain Inspection Department for grading. 
No change in grade resulted from the use of this dust. 

Table 1. --Average moisture content and numbers of insects found in 
wheat stored in wooden farm bins in experimental series, Reno, 
County, Kans., 1951 




Number of insects per 
1,000 grams of wheat in-- 







None (controls) 
Fumigation in August 







DDT spray on walls 







Synergized pyrethrum 
spray on walls 







Synergized pyrethrum 
dust in wheat 






Synergized pyrethrum 
spray on walls; 
synergized pyrethrurr 
dust in wheat 






1/ Before fumigation. 


iiiii him 111 ii 

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